The present invention relates to the art of non-invasive anatomical condition examination. It finds particular application in conjunction with cardiac gated magnetic resonance imaging and will be described with particular reference thereto. However, it is to be appreciated that the invention may find application in other non-invasive examination techniques in which conductive leads extend through changing magnetic fields.
Magnetic resonance imaging sequences commonly include the application of a radio frequency pulse concurrently with a slice select magnetic field gradient pulse. A phase encode magnetic field gradient pulse encodes phase into the nuclei induced resonance by the radio frequency pulse. Another radio frequency pulse is applied to invert the magnetic resonance and cause a magnetic resonance echo. The echo is read in the presence of a read magnetic field gradient pulse. Dephasing magnetic field gradient pulses in the slice select and read direction are commonly applied with an opposite polarity between the slice select and read gradient pulses. This sequence is repeated a multiplicity of times, each time with a different amplitude phase encode magnetic field gradient in order to generate a corresponding multiplicity of differently phase encoded views.
Anatomical movement, such as cardiac and respiratory motion, tends to degrade the resultant images. The amount of degradation is related to the amount or magnitude of physiological displacement from view to view, the rate of movement, and the like. Various anatomical condition monitors have been utilized to control the collection, processing, or use of magnetic resonance and other non-invasive imaging data in accordance with physiological motion. See for example, U.S. Pat. Nos. 4,763,075 to Weigert and 4,545,384 to Kawachi.
A patient's cardiac cycle is normally sensed with electro-cardiographic electrodes mounted to the patient's skin and connected by electrically conductive leads to processing circuitry. The electrodes commonly include a silver halide electrically conductive film which is covered by a thin layer of electrically conductive gel impregnated foam to assure good electrical connection with the patient's skin. An adhesive pad surrounds the electrode to hold it firmly and securely to a selected portion of the patient's skin. The silver halide film is connected with a metallic detent which is snap fit into a corresponding conductive clip or socket at the end of each lead.
On occasion, patients complain of a burning sensation under the cardiac electrodes during a magnetic resonance examination. When the electro-cardiographic electrode pads are removed, red marks are sometimes visible on the patient's skin. Although these marks were originally attributed to an allergic reaction to the electrically conductive gel or irritation from the adhesives, there is now evidence that patients have actually been burned by the pads. See Kanal, et al., Radiology 176:593-606, 1990.
The present invention contemplates a new and improved construction for the prevention of localized heating under cardiac electrodes and a method for the sensing of skin temperature in order to effect monitoring of the patient's skin temperature.